External Harddrive Query

I've been booting most of my games using my external harddrive ( a 2TB seagate, with external power supply ). No complaints so far

Just today, I was gifted a 1TB Seagate external harddrive ( just plug and play, no external power supply ).

Question - Am I better off, in sticking with the pattern of booting my games using the 2TB external ( with power supply ), or is there no tangible difference between the two ? I figured the external supply gave the harddrive some essence of stability, versus the stand-alone hd without the power supply.

I ask, mainly because ,although I'd love to use the new 1TB seagate as my primary gaming harddrive, I'm limited in my ability to shrink the partition to anything larger than 400 gb when I actually want at least 800 gb ( I normally shrink the partition, convert the unallocated space into a partition, and convert the new partition to FAT32. For the new harddrive, the only way I can get more than 400 gb, is if I defragment the disk, and run some other missions ).

If the 2tb harddrive (with power) is a safer bet , I'd rather not bother at all and just stick with the old pattern. I figured most of you guys would be booting games off an external, so any advice would be greatly appreciated